Bump to PHP 8.1 and add missing return types

Bump to PHP >= 7.1

Allow the installation on php 8.

bug symfony#88 Do not use PreFileDownloadEvent from Composer (emodric)

This PR was merged into the 1.2-dev branch.

Discussion
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Do not use PreFileDownloadEvent from Composer

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72e6652 Do not use PreFileDownloadEvent from Composer

Fix issue on Composer 2

fix typo

bug symfony#85 Add support for composer-plugin-api v2 (Ayesh)

This PR was merged into the 1.2-dev branch.

Discussion
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Add support for composer-plugin-api v2

Composer version 2 has `composer-plugin-api` version 2, and this plugin attemts to support both API versions.

See [What's new in Composer 2](https://php.watch/articles/composer-2) and [UPGRADE-2.0](https://github.com/composer/composer/blob/master/UPGRADE-2.0.md#for-integrators-and-plugin-authors) for more changes in API.

 - Empty methods `\Symfony\Thanks\Thanks::deactivate()` and `\Symfony\Thanks\Thanks::uninstall()` are added to make it compatible both versions.
 - On Composer v2, `\Hirak\Prestissimo\CurlRemoteFilesystem` is not used in favor of Composer's native `\Composer\Util\HttpDownloader` which make multiple Curl connections.

Related: symfony#84 and composer/composer#8726.

`thanks` 🙏

Commits
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7502bef Add support for composer-plugin-api v2

bug symfony#80 Fetch funding links when needed + fail gracefully (nic…

…olas-grekas)

This PR was merged into the 1.2-dev branch.

Discussion
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Fetch funding links when needed + fail gracefully

Closes symfony#79

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59ec80b Fetch funding links when needed + fail gracefully

bug symfony#77 Fix reporting failures when there is only one (nicolas…

…-grekas)

This PR was merged into the 1.2-dev branch.

Discussion
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Fix reporting failures when there is only one

Commits
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1baf7fc Fix reporting failures when there is only one

bug symfony#76 Don't register "fund" command when composer already ha…

…s one (nicolas-grekas)

This PR was merged into the 1.2-dev branch.

Discussion
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Don't register "fund" command when composer already has one

As suggested in symfony#73 (comment)

Commits
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6ca6fb7 Don't register "fund" command when composer already has one